Gas sensing system and method

ABSTRACT

Systems and methods for sensing gas are disclosed. In one aspect, a system to monitor an output of a gas source comprises a chamber comprising a plurality of input ports to receive inputs from a plurality of gas sources, and means for repeatedly blocking one of the plurality of input ports for a period of time, detecting which one of the plurality of input ports is blocked, collecting data from a plurality of samples from the enclosure while the one of the plurality of input ports is blocked, and storing the data in a memory in association with an indicator of which one of the plurality of input ports is blocked. Other embodiments may be described.

BACKGROUND

The subject matter described herein relates to gas sensor systems formonitoring of gases.

In various applications it may be useful to monitor attributes of onegas source in a plurality of gas sources. For example, some aircraftinclude an air separation unit (ASU) which has a plurality of airseparation modules (ASMs). The ASMs supply an inert gas such as nitrogento a fuel tank to maintain inerting in the tank as fuel is consumed bythe aircraft. The inert gas may also be supplied to systems other thanfuel tanks.

Existing measurement systems route the output of ASMs through a gassensor to determine the relative amounts of gas in the output flow ofthe ASMs. For example, the amount of oxygen in the combined output flowmay be measured. If the amount of oxygen in the combined output exceedsa predetermined threshold, then its possible that all the ASMs may be,repaired, or replaced, even though only one of the ASMs requireservicing. Accordingly, systems and methods to sense gas from a singlegas source in a multi-source system may find utility.

SUMMARY

In one aspect, a system to monitor an output of a gas source comprises achamber comprising a plurality of input ports to receive inputs from aplurality of gas sources, and means for repeatedly blocking one of theplurality of input ports for a period of time, detecting which one ofthe plurality of input ports is blocked, collecting data from aplurality of samples from the enclosure while the one of the pluralityof input ports is blocked, and storing the data in a memory inassociation with an indicator of which one of the plurality of inputports is blocked.

In another aspect, an aircraft comprises a fuselage and a system tomonitor an output of a gas source comprises a chamber comprising aplurality of input ports to receive inputs from a plurality of gassources, and means for repeatedly blocking one of the plurality of inputports for a period of time, detecting which one of the plurality ofinput ports is blocked, collecting data from a plurality of samples fromthe enclosure while the one of the plurality of input ports is blocked,and storing the data in a memory in association with an indicator ofwhich one of the plurality of input ports is blocked.

In another aspect, a method to monitor an output of a gas source,comprises receiving inputs from a plurality of gas sources in aplurality of input ports in a chamber, repeatedly blocking one of theplurality of input ports for a period of time, detecting which one ofthe plurality of input ports is blocked, collecting data from aplurality of samples from the enclosure while the one of the pluralityof input ports is blocked, and storing the data in a memory inassociation with an indicator of which one of the plurality of inputports is blocked.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of methods and systems in accordance with the teachings ofthe present disclosure are described in detail below with reference tothe following drawings.

FIG. 1 is a schematic, high-level illustration of a gas sensing systemto detect, according to aspects.

FIGS. 2-4 are schematic top views of chambers which may be used in a gassensing system, according to aspects.

FIG. 5 a schematic illustration of a processing device, according toaspects.

FIG. 6 is a flowchart illustrating operations in a gas sensing method,according to aspects.

FIG. 7 is a schematic illustration of an aircraft, according to aspects.

DETAILED DESCRIPTION

Specific details of certain embodiments are set forth in the followingdescription and the associated figures to provide a thoroughunderstanding of such embodiments. One skilled in the art willunderstand, however, that alternate embodiments may be practiced withoutseveral of the details described in the following description.

The invention may be described herein in terms of functional and/orlogical block components and various processing steps. For the sake ofbrevity, conventional techniques related to data transmission,signaling, network control, and other functional aspects of the systems(and the individual operating components of the systems) may not bedescribed in detail herein. Furthermore, the connecting lines shown inthe various figures contained herein are intended to represent examplefunctional relationships and/or physical couplings between the variouselements. It should be noted that many alternative or additionalfunctional relationships or physical connections may be present in apractical embodiment.

The following description may refer to components or features being“connected” or “coupled” or “bonded” together. As used herein, unlessexpressly stated otherwise, “connected” means that one component/featureis in direct physically contact with another component/feature.Likewise, unless expressly stated otherwise, “coupled” or “bonded” meansthat one component/feature is directly or indirectly joined to (ordirectly or indirectly communicates with) another component/feature, andnot necessarily directly physically connected. Thus, although thefigures may depict example arrangements of elements, additionalintervening elements, devices, features, or components may be present inan actual embodiment.

Described herein are examples of systems and methods for gas sensing.More particularly, the systems and methods described herein enable thesensing of gas output from a single gas supply source in a multi-sourcesystem. In brief, a chamber is provided with a plurality of input ports,each of which receives a gas input from a gas source in a multi-sourcesystem. One of the input ports is blocked for a period of time and datais collected from the remaining input sources. The data is stored inassociation with an indicator of which input port was blocked while thedata was collected. This process is then repeated in a pseudo-randomfashion to collect a robust data set. A processing device may be used toanalyze the data to determine a gas measurement from the input ports,which correspond to the respective gas sources.

FIG. 1 is a schematic, high-level illustration of a gas sensing systemaccording to aspects. Referring to FIG. 1, in some aspects a system tomonitor a composition of a gas comprises a chamber 110 which comprises aplurality of input ports 112 configured to received a potion of gas froma plurality of gas sources 130A, 130B, 130C, which may be referred tocollectively herein by reference numeral 130.

The particular shape and size of chamber 110 may be determined at leastin part by the parameters (e.g., gas flow and pressure) of the gasmonitoring system 100. Chamber 110 may include one or more vents toallow gas directed into the chamber 110 via input ports 112 to be ventedfrom the chamber 110.

The specific example system depicted in FIG. 1 includes three gassources, but it will be understood that other examples may include moreor fewer gas sources 130. The gas sources 130 may be coupled to a remotesystem or device via output lines 132A, 132B, 132C, which may bereferred to collectively herein by reference number 132. The outputlines 132 comprise respective feed lines 134A, 134B, 134C, which may bereferred to collectively herein by reference numeral 134, coupled toinput ports 112 of chamber 110. In some examples the system 110 furtherincludes one or more position sensors 140. Additional details of thechamber 110 will be described below with reference to FIGS. 2-4.

System 100 further comprises at least one gas sensor 150 positioned tomonitor the gas in chamber 110. The particular type of gas sensor 150may be a product of the gas or gases that system 100 is monitoring. Forexample, in the ASM application described above the gas sensor 150 maybe an oxygen sensor which may be configured to detect the amount ofoxygen in the gas in chamber 110. In other examples the gas sensor 150may be any of a number of combustible, flammable and toxic gases andvapors such as Carbon Dioxide, Carbon Monoxide, Ozone, LiquefiedPetroleum Gas (Propane, Butane, etc.), Combustibles (fuel vapors, etc.)Alcohol, Hydrogen, Smoke, Hydrogen Sulfide, Chlorine, Chlorine Dioxide,Sulfur Dioxide, Nitrogen Dioxide, Ammonia, Hydrogen Chloride, HydrogenFluoride, Nitric Oxide, Hydrogen Cyanide, Ethylene Oxide and the like.

System 100 further includes a processing device 160 communicativelycoupled to the position sensor(s) 140 and the gas sensor(s) 150.Additional details of the processing device 160 are described withreference to FIG. 5, below.

FIGS. 2-4 are schematic top views of chambers 110 which may be used in agas sensing system, according to aspects. In some examples the chamber110 may be configured to block, in a pseudo-random fashion, one of theplurality of input ports 112 for a period of time. In the exampledepicted in FIG. 2 the chamber 110 presents a triangular cross-sectionalshape and comprises three sloped surfaces 114 on the floor of thechamber 110 that intersect at a peak 115. The input ports 112 arepositioned proximate to the corners, which are the low points, of therespective sloped surfaces 114 of the floor.

A ball 116 is disposed within chamber 110 and able to roll relativelyfreely on the sloped surfaces 114 of the chamber 110. In someembodiments the ball 116 may comprise a ferrous material, e.g., steel orthe like. Position sensors 140 may be positioned proximate the inputports 112 to detect when the ball 116 is positioned over the input port112. In some examples the position sensors 114 may be embodied as Halleffect sensors.

In operation the chamber of FIG. 2 may be positioned such that the planeestablished by the three corners of the floor is approximately level(i.e., parallel to the earth) so that the force of gravity tends to pullthe ball 116 into a corner of the chamber 110, such that the ball 116blocks one of the input ports 112. The ball 116 may be movedperiodically by subjecting the chamber 110 to acceleration. For example,in a vehicle such as a waterborne vehicle the chamber 110 may beaccelerated as a result of motion due to waves or the like. Similarly,in a land-based vehicle chamber 110 may be accelerated as a result ofmotion due to starting and stopping the vehicle, turning, or hittingbumps on a road. In an airborne vehicle chamber 110 may be acceleratedas a result of motion due to taking off, landing, turning, orturbulence. In an example in which the chamber 110 is used in astationary environment the chamber 110 may be mounted on or coupled to avibrating element, e.g., a vibrating platform or the like, which may beactivated on a periodic basis.

In response to acceleration of the chamber 110 the ball 116 may roll onthe sloped surfaces 114, eventually coming to rest under the force ofgravity in one of the corners such that ball 116 blocks an input port112. Thus, the combination of the sloped surfaces 114 and the ball 116provide a mechanism to block, in a pseudo-random fashion, one of theplurality of input ports 112 in the chamber 110. The position sensor 140proximate the input port 140 detects that the ball is blocking the inputport and, in response thereto, generates a signal which is communicatedto processing device 160.

It will be recognized that while the chamber 110 depicted in FIG. 2 hasthree sloped surfaces 114, in other examples the chamber 110 may beprovided with more or fewer sloped surfaces 114. The particular numberof sloped surfaces is not critical and may be, at least in part, afunction of the number of input ports 112 to be monitored. Further,while a preferred embodiment may include a slopped surface otherembodiments may be envisaged such as a flat floor or a floor havingsloped surfaces with the input port 112 in a central position withrespect to the floor area. Further, other embodiments may includemultiple balls or devices to block the input ports.

The example depicted in FIG. 3 uses a technique similar to the exampledepicted in FIG. 2 to block, in a pseudo-random fashion, one of theplurality of input ports 112 in the chamber 110. Referring to FIG. 3,the chamber 110 comprises a plurality of structures 118 which define aplurality of discrete sections 120A, 120B, 120C, which may be referredto collectively herein by reference numeral 120. The input ports 112 arepositioned in the respective sections 120, and the floor of the chamber110 may be sloped such that the input ports 112 are at the low point ofthe chamber.

As described above, the ball 116 may be moved due to acceleration andwill settle, under the force of gravity, back into one of the sections120, thereby blocking, in a pseudo-random fashion, one of the pluralityof input ports 112 for a period of time. The position sensor 140proximate the input port 140 detects that the ball 116 is blocking theinput port and, in response thereto, generates a signal which iscommunicated to processing device 160.

It will be recognized that while the chamber 110 depicted in FIG. 3 hastwo structures 118 which define three sections 120, in other examplesthe chamber 110 may be provided with more or fewer structures 118defining more or fewer sections 120. The particular number of sections120 is not critical and may be, at least in part, a function of thenumber of input ports 112 to be monitored.

In the example depicted in FIG. 4 the chamber 110 may comprise aplurality of input ports 112 which can be selectively opened and closedby a valve or regulator which may be controlled by a remote device suchas processing device 160. For example, processing device 160 maycomprise logic to selectively close one of the input ports 112 in eithera pseudo-random or an ordered fashion. The input port 112 may remainclosed for a predetermined period of time, which may also be determinedin a pseudo-random fashion. For example, the processing device 160 mayutilize a random number generator to select an input port 112 to closeand to select a period of time to keep the port closed or use apredetermined time value. After the time period elapses the processingdevice may utilize the random number generator or a predeterminedsequence to close another input port. The example depicted in FIG. 4does not require position detectors 140 because the processing device160 selects the input port 112 to close.

As described above, position sensor(s) 140 and the gas sensor(s) 150 maybe coupled to a processing device 160. In some embodiments theprocessing device 160 may be implemented as a general purpose computingsystem. FIG. 5 is a schematic illustration of a computing system 500that may be used to monitor for airborne impurities. In someembodiments, system 500 includes a computing device 508 and one or moreaccompanying input/output devices including a display 502 having ascreen 504, one or more speakers 506, a keyboard 510, one or more otherI/O device(s) 512, and a mouse 514. The other I/O device(s) 512 mayinclude a touch screen, a voice-activated input device, a track ball,and any other device that allows the system 500 to receive input from auser.

The computing device 508 includes system hardware 520 and memory 530,which may be implemented as random access memory and/or read-onlymemory. A file store 580 may be communicatively coupled to computingdevice 508. File store 580 may be internal to computing device 508 suchas, e.g., one or more hard drives, CD-ROM drives, DVD-ROM drives, orother types of storage devices. File store 580 may also be external tocomputer 508 such as, e.g., one or more external hard drives, networkattached storage, or a separate storage network.

System hardware 520 may include one or more processors 522, videocontrollers 524, network interfaces 526, and bus structures 528. In oneembodiment, processor 522 may be embodied as an Intel® Pentium IV®processor available from Intel Corporation, Santa Clara, Calif., USA. Asused herein, the term “processor” means any type of computationalelement, such as but not limited to, a microprocessor, amicrocontroller, a complex instruction set computing (CISC)microprocessor, a reduced instruction set (RISC) microprocessor, a verylong instruction word (VLIW) microprocessor, or any other type ofprocessor or processing circuit.

Graphics controller 524 may function as an adjunction processor thatmanages graphics and/or video operations. Graphics controller 524 may beintegrated onto the motherboard of computing system 500 or may becoupled via an expansion slot on the motherboard.

In one embodiment, network interface 526 could be a wired interface suchas an Ethernet interface (see, e.g., Institute of Electrical andElectronics Engineers/IEEE 802.3-2002) or a wireless interface such asan IEEE 802.11a, b or g-compliant interface (see, e.g., IEEE Standardfor IT-Telecommunications and information exchange between systemsLAN/MAN—Part II: Wireless LAN Medium Access Control (MAC) and PhysicalLayer (PHY) specifications Amendment 4: Further Higher Data RateExtension in the 2.4 GHz Band, 802.11G-2003). Another example of awireless interface would be a general packet radio service (GPRS)interface (see, e.g., Guidelines on GPRS Handset Requirements, GlobalSystem for Mobile Communications/GSM Association, Ver. 3.0.1, December2002).

Bus structures 528 connect various components of system hardware 528. Inone embodiment, bus structures 528 may be one or more of several typesof bus structure(s) including a memory bus, a peripheral bus or externalbus, and/or a local bus using any variety of available bus architecturesincluding, but not limited to, 11-bit bus, Industrial StandardArchitecture (ISA), Micro-Channel Architecture (MSA), Extended ISA(EISA), Intelligent Drive Electronics (IDE), VESA Local Bus (VLB),Peripheral Component Interconnect (PCI), Universal Serial Bus (USB),Advanced Graphics Port (AGP), Personal Computer Memory CardInternational Association bus (PCMCIA), and Small Computer SystemsInterface (SCSI).

Memory 530 may include an operating system 540 for managing operationsof computing device 508. In one embodiment, operating system 540includes a hardware interface module 554 that provides an interface tosystem hardware 520. In addition, operating system 540 may include afile system 550 that manages files used in the operation of computingdevice 508 and a process control subsystem 552 that manages processesexecuting on processing device 160.

Operating system 540 may include (or manage) one or more communicationinterfaces 544 that may operate in conjunction with system hardware 520to transceive data packets and/or data streams from a remote source.Operating system 540 may further include a system call interface module542 that provides an interface between the operating system 540 and oneor more application modules resident in memory 530. Operating system 540may be embodied as a UNIX operating system or any derivative thereof(e.g., Linux, Solaris, etc.) or as a Windows® brand operating system, orother operating systems.

In one embodiment, memory 530 includes a monitoring module 540 to managegas monitoring operations of the system 100. The monitoring module 540may include logic instructions encoded in a computer-readable storagemedium which, when executed by processor 522, cause the processor 522 tomanage the system 100 to monitor gas components in chamber 110.

FIG. 6 is a flowchart illustrating operations in a method detectairborne impurities, according to embodiments. Referring to FIG. 6, atoperation 610 it is determined which input port 112 in chamber 110 isblocked. As described above, in some examples the position sensors 140may generate signals which indicate which input port 112 in the chamber110 is blocked. Alternatively, in the example depicted in FIG. 4 theprocessing device 160 controls the input ports 112 such that theprocessing device 160 is aware which input port 112 is closed.

At operation 615 gas sample data is obtained by a gas sensor 150. Asdescribed above, the gas sensor 150 may sense one or more attributes ofa gas in the chamber 110. By way of example, if sensor 150 were anoxygen sensor then sensor 150 may detect a concentration of oxygen inthe chamber 110. The processing device 160 may query the gas sensor 150on a periodic basis, e.g., between about 100 milliseconds and 2000milliseconds.

At operation 620 the gas sample data obtained in operation 615 is storedin association with an indicator of the input port 112 which was blockedwhile the sample data was collected. For example, the gas sample datamay be stored in a data table or the like in memory 530 of processingdevice 160.

At operation 625 it is determined whether the sampling of the blockedport was successful. In some examples, the sampling may be consideredsuccessful if the blocked port is not open during sampling, e.g., due tomovement of ball 116, and if the sampling duration continued for anadequate period of time. If, at operation 625, the sampling the blockedinput port was not successful then control passes back to operation 615and the sampling process continues. Thus, operations 615-625 define aloop pursuant to which processing device 160 may collect gas datasamples from gas sensor 150.

By contrast, if at operation 625 the number of samples exceeds thethreshold then control passes to operation 630. If, at operation 630 athreshold number of gas data samples have not been taken with all inputports 112 in the enclosure 110 blocked then control passes to operation635 and a different input port is blocked. The threshold may be set as apredetermined number and may be static or dynamic. Further, thethreshold may be a function of the number of input ports 112 in thechamber. In some examples the threshold may vary between about 12samples and 100 samples. In the example chambers depicted in FIGS. 3-4the processing device may have to wait for the ball 116 to be movedunder the force of acceleration. By contrast, in the example depicted inFIG. 5 the processing device 160 may continue closing input ports 112 ina pseudo-random or ordered fashion until all input ports 112 have beenclosed.

By contrast, if at operation 630 a threshold number of gas data sampleshave been taken with all input ports 112 in the enclosure 110 blockedthen control passes to operation 640 and the processing device 160determines a characteristic of the gas from the respective input ports112. In some examples, the processing device 160 may first determine anaverage of the gas sample data collected while each input port 112 wasblocked. For example, if the processing device 160 is configured tocollect 100 data samples for each blocked input port 112 then an averageof the 100 data samples is determined. The total output (I_(t)) of theinput ports may be determined by

$\begin{matrix}{I_{T} = \frac{\sum\limits_{i = 1}^{n}\; H_{i}}{n - 1}} & {{EQ}\mspace{14mu} (1)}\end{matrix}$

And the output of any given input port 112 may be determined by

$\begin{matrix}{I_{i} = \frac{\left( {2 - n} \right){\sum\limits_{i = 1}^{n}\; H_{i}}}{n - 1}} & {{EQ}\mspace{14mu} (2)}\end{matrix}$

Where:

I_(t) is the total output from all input ports 112 combined

I_(i) is a total output from a the i^(th) input port;

n is a total number of input ports;

H_(i) is average of measures taken while the i^(th) input port isblocked.

Thus, the system 100 described herein enables gas sample data to becollected from chamber 110 while the input ports 112 are blocked in apseudo-random fashion. The processing device 160 may then determine acharacteristic (i.e. a composition) of the gas associated with any giveninput port 112. This output may be stored in a computer-readable mediumsuch as memory 130 or presented on a user interface, thereby allowing auser to ascertain information about a single gas source 130 in amulti-source system, thereby eliminate the need for multiple expensivesensors and the power and weight requirements needed to support thesensors.

While various embodiments have been described, those skilled in the artwill recognize modifications or variations which might be made withoutdeparting from the present disclosure. For example, while the processingdevice 160 is described as a fully functioning computer system, it willbe recognized that the processing device 160 may be embodied as aspecialized controller, e.g., an application specific integrated circuit(ASIC) or a field programmable gate array (FPGA).

In some embodiments a system 100 may be incorporated into compartmentsof on an aircraft 700, such as an airplane, helicopter, spacecraft orthe like. In alternate embodiments a system 100 may be incorporated intoa ground-based vehicle such as a truck, tank, train, or the like, or ona water-based vehicle such as a ship. In further embodiments a system100 may be incorporated into a land-based device or system.

The examples illustrate the various embodiments and are not intended tolimit the present disclosure. Therefore, the description and claimsshould be interpreted liberally with only such limitation as isnecessary in view of the pertinent prior art.

What is claimed is:
 1. A system to monitor an output of a gas source,comprising: a chamber comprising a plurality of input ports configuredto receive a flow of gas from a plurality of gas sources; means forrepeatedly: temporarily blocking one of the plurality of input ports;detecting the input port that is blocked; sampling, from a sensor, acharacteristic of the gas in the chamber; and storing data from thesensor in a memory in association with an indicator of which one of theplurality of input ports is blocked;
 2. The system of claim 1, wherein:the chamber comprises a plurality of sloped surfaces, wherein the inputports are positioned on respective sloped surfaces; and the means forrepeatedly blocking one of the plurality of input ports for a period oftime comprises a ball which rolls over the plurality of sloped surfaces.3. The system of claim 1, wherein: the chamber comprises a plurality ofstructures which define a plurality of discrete sections, wherein theinput ports are positioned in the respective sections; and the means forrepeatedly blocking, one of the plurality of input ports for a period oftime comprises a ball which rolls into one of the plurality of discretesections.
 4. The detection system of claim 1, wherein the means forrepeatedly blocking one of the plurality of input ports for a period oftime comprises a network of controllable valves.
 5. The detection systemof claim 1, wherein the means for detecting which one of the pluralityof input ports is blocked comprises a Hall effect position sensor. 6.The system of claim 1, wherein the means detecting a property of the gasin the chamber comprises a gas sensor.
 7. The system of claim 1, furthercomprising means to determine a characteristic of a gas from one of theplurality of input ports from the data.
 8. The system of claim 1,wherein the means to determine an output from the one of the pluralityof input ports from the data comprises a processor-based devicecomprising logic, at least partially including hardware logic, tocompute:$I_{i} = \frac{\left( {2 - n} \right){\sum\limits_{i = 1}^{n}\; H_{i}}}{n - 1}$where: I_(i) is a total output from a the i^(th) input port; n is atotal number of input ports; H_(i) is average of measures taken whilethe i^(th) input port is blocked.
 9. An aircraft comprising: a system tomonitor an output of a gas source on the aircraft, comprising: a chambercomprising a plurality of input ports to receive gas from a plurality ofgas sources; means for repeatedly: temporarily blocking one of theplurality of input ports; detecting which one of the plurality of inputports is blocked; sampling, from a sensor, a characteristic of the gasin the chamber; and storing data from the sensor in a memory inassociation with an indicator of which one of the plurality of inputports is blocked.
 10. The aircraft of claim 9, wherein: the chambercomprises a plurality of sloped surfaces, wherein the input ports arepositioned on respective sloped surfaces; and the means for repeatedlyblocking one of the plurality of input ports for a period of timecomprises a ball which rolls over the plurality of sloped surfaces. 11.The aircraft of claim 9, wherein: the chamber comprises a plurality ofstructures which define a plurality of discrete sections, wherein theinput ports are positioned in the respective sections; and the means forrepeatedly blocking one of the plurality of input ports for a period oftime comprises a ball which rolls into one of the plurality of discretesections.
 12. The aircraft of claim 9, wherein the means for repeatedlyblocking, in a pseudo-random or ordered fashion, one of the plurality ofinput ports for a period of time comprises a network of controllablevalves.
 13. The aircraft of claim 9, wherein the means for detectingwhich one of the plurality of input ports is blocked comprises a Halleffect position sensor.
 14. The aircraft of claim 9, wherein the meansfor collecting data from a plurality of samples from the enclosure whilethe one of the plurality of input ports is blocked comprises a gassensor to collect gas samples from the enclosure.
 15. The aircraft ofclaim 9, further comprising means to determine a characteristic of a gasfrom the one of the plurality of input ports from the data.
 16. Theaircraft of claim 9, wherein the means to determine an output from theone of the plurality of input ports from the data comprises aprocessor-based device comprising logic, at least partially includinghardware logic, to compute:$I_{i} = \frac{\left( {2 - n} \right){\sum\limits_{i = 1}^{n}\; H_{i}}}{n - 1}$where: I_(i) is a total output from a the i^(th) input port; n is atotal number of input ports; H_(i) is average of measures taken whilethe i^(th) input port is blocked.
 17. A method to monitor an output of agas source, comprising: receiving inputs from a plurality of gas sourcesin a plurality of input ports in a chamber; repeatedly: temporarilyblocking one of the plurality of input ports; detecting which one of theplurality of input ports is blocked; sampling, from a sensor, acharacteristic of the gas in the chamber; and storing data from thesensor in a memory in association with an indicator of which one of theplurality of input ports is blocked.
 18. The method of claim 17, furthercomprising determining a characteristic of a gas from the one of theplurality of input ports from the data.
 19. The method of claim 18,wherein: the chamber comprises a plurality of structures which define aplurality of discrete sections, wherein the input ports are positionedin the respective sections; and blocking one of the plurality of inputports for a period of time comprises moving a ball which rolls into oneof the plurality of discrete sections.
 20. The method of claim 18,wherein determining an output from the one of the plurality of inputports from the data comprises computing:$I_{i} = \frac{\left( {2 - n} \right){\sum\limits_{i = 1}^{n}\; H_{i}}}{n - 1}$where: I_(i) is a total output from a the i^(th) input port; n is atotal number of input ports; H_(i) is average of measures taken whilethe i^(th) input port is blocked.